1. Field of the Invention
This invention relates to a fluorescent display device, and more particularly to a graphic fluorescent display device which is capable of improving the quality of the display.
2. Description of the Prior Art
With the diversification of display, a fluorescent display device for effecting graphic display has been extensively put in practice in the art which is adapted to carry out image display such as desired letters, figures and the like in addition to a fluorescent display device of the type of selectively exciting figure eight shaped segment anodes to carry out numerical display.
In general, a fluorescent display device is advantageous in that it can be driven at low voltage with less power consumption, formed in a flat shape and provide luminous display which is readily observed. Thus, it is expected to be much in demand as a display device for terminal components in various types of information system in place of a cathode ray tube.
Although a graphic display system using a fluorescent display device may employ various electrode structures, an X-Y matrix drive structure is generally employed in view of easiness in manufacture, the number of external lead wires, facility in operation, and the like which is constructed in a manner to arrange control electrodes in the direction across that of arrangement of anodes, and adapted to scan the control electrodes in a time-sharing manner and supply a display signal to a desired row of the anodes in synchronism with the scanning of the control electrodes.
A typical electrode structure of such type is shown in FIG. 1. In the electrode structure shown in FIG. 1, phosphor-coated anodes A are connected together by a wiring conductor every row and control electrodes G are arranged in the column direction of the anodes A. The control electrode G are scanned in a time-sharing manner and a display signal is supplied to the anodes A via the wiring conductor C. Further, electrons emitted from a cathode (not shown) impinge on the anode positioned at the intersection between a selected row of the anodes A and the control electrodes to excite the phosphor deposited on the anode A to carry out the light-emission.
However, in the fluorescent display device shown in FIG. 1, it is substantially difficult to arrange the anodes in the column direction at narrow intervals, because it is required to arrange the control electrodes of a mesh-like shape opposite to each column of the anodes, which results in the arrangement of the anodes with a high density being substantially impossible. Further, the construction of the fluorescent display device shown in FIG. 1 causes the unselected control electrodes to be kept at negative potential with respect to the cathode, and the path of electrons to the anodes A is affected by a negative electric field generated by the unselected control electrode of negative potential adjacent to the selected control electrode. This results in the electrons failing to uniformly impinging on the overall surface of the anode A, to thereby cause a display defect.
In order to eliminate the above-described disadvantages of the fluorescent display device shown in
FIG. 1, the inventors previously proposed a graphic fluorescent display device as shown in
FIG. 2, which is now U.S. Pat. No. 4,459,514, issued July 10, 1984.
The fluorescent display device shown in FIG. 2 is constructed in such a manner that anodes conductors are arranged in parallel in a stripe shape in the row direction within a display region, a phosphor is deposited on each of the anode conductors to form an anode SA, and control electrodes G (G1, G2 - - - ) are arranged in the column direction with respect to the anodes SA.
In the operation of the fluorescent display device shown in FIG. 2, adjacent two of the control electrodes are selectively scanned together while shifting selection of the control electrodes one by one in order or two of the control electrodes are scanned together in order of G1 and G2, G2 and G3, G3 and G4 - - - , and a display signal is supplied to the anodes SA in synchronism with the scanning of the control electrodes so that luminous display may be carried out by a picture cell constituted by a region on the anode interposed between the two control electrodes, for example, a region P shown in FIG. 2.
The fluorescent display device shown in FIG. 2 can be easily manufactured because of its simplified control electrode structure. Also, it does not cause a display defect since one picture cell is formed by a region controlled by the adjacent two control electrodes G.
A fluorescent display device of the type shown in FIG. 2 is required to carry out display of a high quality as well as display of a high density and any display in the form of letters, figures and the like. For this purpose, it is indispensable to substantially prevent the occurrence of dark areas called dark lines or high luminance areas called bright lines between plural cathodes stretchedly arranged. This is accomplished, for example, by narrowing the interval between each adjacent cathodes in relation to the distance between the cathodes and the control electrodes or by providing an electrode means for diffusing electrons emitted from the cathodes on the surface of a casing of the display device opposite to the anodes with the control electrodes and cathodes being interposed between the surface and the anodes. These are effective to eliminate the dark lines or bright lines between the cathodes.
It has been found, however, that the fluorescent display device shown in FIG. 2 has a factor adversely affecting the quality of display other than the problem of dark lines or bright lines as described above. More particularly, when the cathodes K are stretchedly arranged in the direction parallel to the anodes SA, a streak pattern D of non-uniform brightness occurs right below the cathodes K which appears to correspond to the shade of the control electrode G.
The formation of such streak pattern D would be due to that the adjacent two control electrodes G selected and scanned form a sort of electrostatic lens, which deflects electrons emitted from the cathodes K right below the cathodes K to cause the non-uniform stream of electrons at the areas right below the control electrodes G and at the peripheries thereof. Particularly, the streak pattern D is an obstacle to display when increasing a light-emission area of a display region or when carrying out inversion display or display carried out by emitting light from picture cells forming the background and using non-luminous picture cells.
Accordingly, the problem of the streak pattern is not solved by arranging the cathodes at a narrow interval between each adjacent cathodes or the like. Thus, it is highly desired to develop a fluorescent display device which is capable of eliminating the problem.